* You specify the individual ports using the Indentifier "Monitor-''port''" lines in the Monitor sections. These are the same ports that are listed by "xrandr -q" and are also found in /var/log/Xorg.0.log

+

* You specify the individual ports using the Indentifier "Monitor-''port''" lines in the Monitor sections. These are the same ports that are listed by "xrandr -q".

* This setup does not specify which resolutions to use or absolute positions relative to each other of both monitor's images. To solve this you could add a preferred mode and position to the "Monitor" sections:

* This setup does not specify which resolutions to use or absolute positions relative to each other of both monitor's images. To solve this you could add a preferred mode and position to the "Monitor" sections:

Revision as of 01:12, 23 April 2012

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Background

Xwindows drives the underlying graphical interface of most if not all Unix/Linux computers providing a GUI. It was developed in 1984 at MIT. After around 35 years of development, tweaking and adding of new hardware and ideas, it is generally acknowledged to be a bit of a beast. It should be remembered that the common configuration at time of development was a single mini running X providing individual views to Xterminals in a timesharing system. Nowadays the norm is X providing a single screen on a desktop or laptop.

All of this means that there are many ways of achieving the same thing and many slightly different things that can meet the same purpose. In modern X versions sometimes you can get away with limited or no configuration. In the last few years the boast is that X is self configuring. Certainly the best practice rule of thumb is less configuration is better - that is only configure what is wrong.

Extended Screen

This approach works well when the monitors are the same size and resolution. Interesting things happen - like windows off screen etc - when they are not. It is supposed to work but does not. It should also be noted that in a full desktop environment such as Gnome there are built-in GUI utilities to achieve this. However *box environments suffer.

4) Note down the portnames of the monitors attached - in the case of the above "VGA1" and "HDMI1"

5) Decide which resolution you are going to use. Each monitor has a preferred mode that, according to the manufacturer, is the best visually. These are marked by a "+". The mode a monitor is running at is marked by a "*". You should if possible use the preferred mode and a mode shared by both monitors. You can also add modes: see the Xrandr page.

6) Decide which monitor is on the left or right (or top and bottom) and configure as follows:

VGA1 below HDMI1 at 1024x768

--above places the previous screen (HDMI1) to the above the specified screen (VGA1)

7) Play around at the command line until you have a setting that works for you. When you do simply copy that call to xrandr into your window manager/desktop startup file. Arandr is a GUI interface to xrandr and may have some benefits in your search for a solution.

I found that some settings and approaches worked better than others and that even the best did not work in all cases because of the differences between my two monitors.

Extended Screen on the Intel Driver

Another way to set up dual-heads is by using an xorg.conf file. The following does this with the intel driver as the example. This configuration should work with most Intel setups.

For information on the intel driver see its manpage:

man intel

The following is an X-Server configuration and is made as a file named "xorg.conf", in the filesystem here:

/etc/X11/xorg.conf

Setting up a dual-head configuration with an Intel driver you only need three sections as follows:

You specify the individual ports using the Indentifier "Monitor-port" lines in the Monitor sections. These are the same ports that are listed by "xrandr -q".

This setup does not specify which resolutions to use or absolute positions relative to each other of both monitor's images. To solve this you could add a preferred mode and position to the "Monitor" sections:

Option "PreferredMode" "1920x1080"
Option "Position" "0 0"

Setting up the Intel dual-head this way uses "xrandr". On the Multihead page there is another method to configure the xorg.conf file called Xinerama. Xinerama is an older way of doing the setup and xrandr should be preferred over it if possible.

Extended Screen on other cards

The wiki has an excellent discussion of dual monitors for ATI and Nvidia chipsets in the Xorg article.